BLOOD-BRAIN BARRIER - EVIDENCE FOR ACTIVE CATION TRANSPORT BETWEEN BLOOD AND EXTRACELLULAR FLUID OF BRAIN

The concentration gradients of Mg++ and K+ in the cerebrospinal fluid system indicate that the (Mg++) is higher and the (K+) is lower in the extracellular fluid of the cerebral cortex than the concentrations of these cations in either plasma-dialysate or cisternal fluid. Such cation distribution demonstrates the existence of an active transport process across the blood-brain barrier.